fed chairman ben bernanke expects the economy to grow and unemployment to fall. but he also signalled today that years of low interest rates that have made it easy for companies to invest and families to buy cars and homes may soon be ending. the dow dropped more than 200 points on that news. the nasdaq dropped almost 40. ton, abc news reporter rebecca jarvis explains what that means to the average american. >> david and sara turn bull are looking at homes in newbury park, california, for their expanding family, hoping to take advantage of record low interest rates. >> because we're at a time where we can buy, we would ideally like to lock in an interest rate. >> but in the last six weeks, interest rates have started climbing. mortgages now above 4% for the first time in a year. up more than half a percent since may. >> people are really thinking that makes a big difference in my monthly payment and what i can afford. >> every 1% increase in mortgage rates makes owning a home about 10% more expensive. >> i like that. >> in real terms, when rates rise a percent, t